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The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
The term pharmacology is derived from the Greek words pharmakon("claim, medicine, poison, or remedy") and logos ("study").
Signs of depression include feeling sad most of the time for 2 weeks or longer; loss of interest in things normally enjoyed; lack of energy; sleep and appetite disturbances; weight changes; feelings of hopelessness, helplessness, or worthlessness; an inability to make decisions; and thoughts of death and suicide.
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.